It is known that polysiloxane-polycarbonate block cocondensates have good properties in relation to low-temperature (notched) impact resistance, chemicals resistance and outdoor weathering resistance, and also good ageing properties and flame retardancy. In terms of these properties they are sometimes superior to conventional polycarbonates (homopolycarbonate based on bisphenol A).
Industrial production of these cocondensates mostly proceeds from the monomers by way of the interfacial process with phosgene. It is moreover known that these siloxane cocondensates can be produced by way of the melt transesterification process with use of diphenyl carbonate. These processes have the disadvantage that the plants used are used for the production of standard polycarbonate, and are therefore large. Production of specialized block cocondensates in these plants is often uneconomic because the volume of the said products is relatively small. The starting materials, e.g. the polydimethylsiloxanes, required for the production of the cocondensates can moreover adversely affect the plant, because they can contaminate the plant or the solvent-circulation systems. The production process moreover requires toxic starting materials such as phosgene or, in the case of the melt transesterification process, has high energy consumption.
Production of polysiloxane-polycarbonate block copolymers by way of the interfacial process is known from the literature and is described by way of example in U.S. Pat. Nos. 3,189,662, 3,419,634, DE-OS (German Published Specification) 3 34 782 and EP 122 535.
US 2013/0267665 discloses the production of polysiloxane-polyorgano-block copolymers with use of hydroxyaryloxy-functional siloxanes.
U.S. Pat. No. 5,227,449 describes the production of polysiloxane-carbonate block copolymers by the melt transesterification process from bisphenol, diaryl carbonate, silanol-terminated polysiloxanes and catalyst. Siloxane compounds used here are polydiphenyl- or polydimethylsiloxane telomers having terminal silanol groups. However, it is known that as chain length decreases in an acidic or basic medium, in contrast to diphenylsiloxane having terminal silanol groups, these dimethylsiloxanes having terminal silanol groups have an increasing tendency toward self-condensation, thus inhibiting incorporation into the copolymer. Cyclic siloxanes formed here remain in the polymer and have an extremely problematic effect in applications in the electrical/electronics sector.
All of these processes have the disadvantage of the use of organic solvents in at least one step of the synthesis of the silicone-polycarbonate block copolymers, the use of phosgene as starting material, or inadequate quality of the cocondensate. In particular, the synthesis of the cocondensates starting from the monomers either by the interfacial process or especially by the melt transesterification process is very complicated: in the melt process by way of example it is necessary to avoid use of high vacuum and high temperatures, in order to prevent evaporation, and thus loss, of the monomers. Only in subsequent reaction stages where oligomers with relatively high molar mass have formed, is it possible to use lower pressures and higher temperatures. This means that the reaction must be conducted in a number of stages, and that reaction times are correspondingly long.
There are also known processes that start from commercially available polycarbonates with the aim of avoiding the disadvantages described above. This is described by way of example in U.S. Pat. Nos. 5,414,054, 5,821,321 and 6,066,700. Here, a conventional polycarbonate is reacted with a specific polydimethylsiloxane in a reactive extrusion process. These processes have the disadvantage of use of high-activity transesterification catalysts which permit production of the cocondensates within short residence times in an extruder. These transesterification catalysts remain in the product, and cannot be deactivated, or can be deactivated only to an inadequate extent. Injection mouldings made of the resultant cocondensates therefore exhibit inadequate ageing performance, in particular inadequate heat-ageing performance. Specialized, and therefore expensive, siloxane blocks must moreover be used.
DE 19710081 describes a process for the production of the abovementioned cocondensates in a melt transesterification process starting from an oligocarbonate and a specific hydroxyarylsiloxane. The said Application also describes the production of the oligocarbonate. However, large-scale industrial production of oligocarbonates is a very complicated approach to the production of relatively small volumes of specific cocondensates. These oligocarbonates have relatively low molecular weights and relatively high terminal OH group concentrations. Because of their low chain length, their phenolic OH concentrations are often above 1000 ppm. Materials of this type are not normally obtainable commercially, and therefore have to be produced specifically for the production of the cocondensates. However, it is uneconomic to operate large-scale industrial plants to produce small volumes of precursors. The impurities present in these precursors, for example residual solvents, residual catalysts, unreacted monomers, etc., moreover make them markedly more reactive than high-molecular-weight commercially available products based on polycarbonate. For these reasons there is no commercial availability of appropriate precursors or aromatic oligocarbonates suitable for the production of these block cocondensates. Furthermore, the process described in DE 19710081 does not permit production of the block cocondensate in short reaction times. Both the production of the oligocarbonate and the production of the block cocondensate proceed by way of a number of stages with residence times totalling well over one hour. The resultant material is moreover unsuitable for production of cocondensates because the final product has poor colour caused by the high concentration of terminal OH groups, and also by other impurities, for example residual catalyst constituents.
Polycarbonate compositions comprising siloxane-containing polycarbonate block cocondensates with good flame retardancy properties are described in the literature, for example in US 2014/329920, US 2013/313493, WO 2013/067684 and WO 2008/060724.
U.S. Pat. No. 6,657,018 describes siloxane-containing block cocondensates. Flame retardants for materials of this type are also described. The block cocondensates in the present Application have a different structure and are not produced conventionally in the interfacial process as in U.S. Pat. No. 6,657,018.
U.S. Pat. No. 5,510,414 describes siloxane-containing block cocondensate blends with polycarbonate and glass fibres which feature transparency or translucent properties. In contrast to this, the compositions involved here are opaque.
US 20070072960 describes specific impact-modified moulding compositions which comprise particular pretreated fillers.
U.S. Pat. No. 7,728,059 describes flame-retardant polycarbonate blends which comprise particular synergistic combinations of various sulphonates.
The abovementioned prior-art moulding compositions are composed of siloxane-containing block cocondensates produced by the interfacial process. In contrast to this, the present Application relates to block cocondensates of specific structure which were produced by way of conventionally obtainable polycarbonates.
Nodera et al. in J. Appl. Pol. Sci. 2006, 102, 1697-1705 say that the siloxane domain size has a large effect on the fire performance of siloxane-containing block cocondensates. The block cocondensates studied by Nodera et al., like the prior-art materials cited above, are produced by the interfacial process. Siloxane domain distributions in block cocondensates produced from commercially available polycarbonates in the melt transesterification process are different from those of materials produced by the interfacial process. It was therefore not obvious that the block cocondensates—produced by the melt transesterification process—used in the present Application have good fire properties.